HARQ is widely supported in current wireless communication standards and devices. From timing relationship, HARQ may be of synchronous type or an asynchronous type. Asynchronous HAQ refers to transmissions (or retransmissions) for a HARQ process may occur at any time and explicit signaling of HARQ process number is required. Synchronous HARQ refers to a case of transmissions (or retransmissions) for a HARQ process, which are restricted to occur at know time instants. Explicit signaling of HARQ process number is not required as the process number may be derived from the sub-frame number. In IEEE® 802.16e design for HARQ both downlink and uplink use asynchronous HARQ. In IEEE® 802.16m design for HARQ, asynchronous HARQ is used in downlink while a synchronous HARQ is used in uplink. HARQ timing contributes to latency and level of uniform acknowledgement channel (ACKCH) distribution.